A novel approach to consolidation of historical limestone: the calcium alkoxides

Potential utilization of calcium alkoxides as stone consolidants was considered. Reaction of Ca(OCH3)2, Ca(OCH2CH3)2(CH3CH2OH)4 and Ca[OCH(CH3)2]2 with the atmosphere in different experimental conditions was studied. The reaction produced CaCO3 and two different pathways seem to be involved, the first taking place through CO2 insertion into the Ca–O bond of Ca(OR)2 species with formation of an alkylcarbonate derivative, subsequently transformed into CaCO3 through ROH elimination; the second takes place through hydrolysis of Ca(OR)2 to Ca(OH)2, which is then carbonated to CaCO3. The vaterite/calcite ratios found in the final CaCO3 vary considerably with the experimental conditions adopted. Investigations demonstrated the potentiality of Ca(OCH3)2 to act as a stone consolidant. In fact, impregnation of a porous substrate, simulating the deteriorated stone, with a methanol solution of Ca(OCH3)2, produced a crystalline vaterite film, which gradually filled all the pores and cavities of substrate and seems to fulfil the necessary requirements for a consolidant. Copyright © 2008 John Wiley & Sons, Ltd.

[1]  E. Weiss,et al.  Die Kristallstrukturen der Erdalkalimethanolate M(OCH3)2, M = Ca, Sr, Ba , 1978 .

[2]  J. Delgado Rodrigues,et al.  Stone consolidation: The role of treatment procedures , 2008 .

[3]  M. Einarsrud,et al.  Shrinkage of silica gels aged in TEOS , 1996 .

[4]  Piero Baglioni,et al.  Colloidal Particles of Ca(OH)2: Properties and Applications to Restoration of Frescoes , 2001 .

[5]  A. Moncrieff.  THE TREATMENT OF DETERIORATING STONE WITH SILICONE RESINS: INTERIM REPORT , 1976 .

[6]  David E. Searle,et al.  Stone deterioration in polluted urban environments , 2004 .

[7]  L. Hubert-Pfalzgraf.  Some trends in the design of homo- and heterometallic molecular precursors of high-tech oxides , 2003 .

[8]  J. Darr,et al.  Insertion reactions of small molecules into group 2 metal alkoxides; structural characterization of , 1998 .

[9]  P. Harrison,et al.  Tin oxide surfaces. Part 13.—A comparison of tin(IV) oxide, tin(IV) oxide–palladium oxide and tin(IV) oxide–silica: an infrared study of the adsorption of carbon dioxide , 1984 .

[10]  Monica Favaro,et al.  Evaluation of polymers for conservation treatments of outdoor exposed stone monuments. Part I: Photo-oxidative weathering , 2006 .

[11]  Monica Favaro,et al.  Evaluation of polymers for conservation treatments of outdoor exposed stone monuments. Part II: Photo-oxidative and salt-induced weathering of acrylic–silicone mixtures , 2007 .

[12]  Marisa Laurenzi Tabasso,et al.  Acrylic Polymers for the Conservation of Stone: Advantages and Drawbacks , 1995 .

[13]  Monica Favaro,et al.  The Four Virtues of the Horta della Carta, Ducal Palace, Venice assessment of the state of preservation and re-evaluation of the 1979 restoration , 2005 .

[14]  R. Snyder,et al.  RIR - Measurement and Use in Quantitative XRD , 1988, Powder Diffraction.

[15]  Kenneth F. B. Hempel,et al.  NOTES ON THE CONSERVATION OF SCULPTURE, STONE, MARBLE AND TERRACOTTA , 1968 .

[16]  K. Hempel.  AN IMPROVED METHOD FOR THE VACUUM IMPREGNATION OF STONE , 1976 .

[17]  C. Rodriguez-Navarro,et al.  Salt weathering: influence of evaporation rate, supersaturation and crystallization pattern , 1999 .

[18]  Clifford Price,et al.  A further appraisal of the ‘lime technique’ for limestone consolidation, using a radioactive tracer , 1988 .

[19]  D. C. Bradley.  Metal alkoxides as precursors for electronic and ceramic materials , 1989 .

[20]  T. Lu,et al.  CO2 fixation and transformation by a dinuclear copper cryptate under acidic conditions. , 2007, Chemistry, an Asian journal.

[21]  F. Andersen,et al.  Infrared spectra of amorphous and crystalline calcium carbonate , 1991 .

[22]  J. Morse,et al.  The dissolution kinetics of major sedimentary carbonate minerals , 2002 .

[23]  George W. Scherer,et al.  Crystallization in pores , 1999 .

[24]  Kris A. Berglund,et al.  In Situ Monitoring of Calcium Carbonate Polymorphs during Batch Crystallization in the Presence of Polymeric Additives Using Raman Spectroscopy , 2003 .

[25]  V. McKee,et al.  Cascade chemistry in azacryptand cages: bridging carbonates and methylcarbonatesElectronic supplementary information (ESI) available: magnetic data. See http://www.rsc.org/suppdata/dt/b1/b110449g/ , 2002 .

[26]  Luigi Dei,et al.  Synthesis of Ca(OH)2 Nanoparticles from Diols , 2001 .

[27]  C. M. Grossi,et al.  Characteristics of carbonate building stones that influence the dry deposition of acidic gases , 1999 .

[28]  O. Lindqvist,et al.  Model study of initial adsorption of SO2 on calcite and dolomite , 2004 .

[29]  Piero Tiano,et al.  Biomediated reinforcement of weathered calcareous stones , 2006 .

[30]  Piero Baglioni,et al.  A New Method for Consolidating Wall Paintings Based on Dispersions of Lime in Alcohol , 2000 .

[31]  K. Fromm,et al.  Structures of alkali and alkaline earth metal clusters with oxygen donor ligands , 2004 .

[32]  Rafael Fort,et al.  Thermodynamic modelling of changes induced by salt pressure crystallisation in porous media of stone , 1999 .